Though binary translation is supported for 64-bit guests on physical AMD hardware, it is not supported for 64-bit nested guests in a virtual machine. 64-bit nested guests can only be run with (virtualized) hardware-assisted virtualization. Unfortunately, fault tolerance for a nested virtual machine requires complete binary translation, because the performance monitor unit of the virtual CPU isn't capable of providing the necessary support for fault tolerance using hardware-assisted virtualization.
In short, you will only be able to run fault tolerance on 32-bit nested virtual machines.